Old English hlæder "ladder, steps," from Proto-Germanic *khlaidri (source also of Old Frisian hledere, Middle Dutch ledere, Old High German leitara, German Leiter), from PIE root *klei- "to lean" (source also of Greek klimax "ladder;" see lean (v.)). In late Old English, rungs were læddrestæfæ and the side pieces were ledder steles. The belief that bad things happen to people who walk under ladders is attested from 1787, but its origin likely is more scientific than superstitious.